Drum, in correct terminology, means an instrument in which the sound is produced by a membrane stretched over the opening of either a frame, or a hollow body of any shape. It is said hollow body which shall be refered to as a drumshell. The materials of construction of drumshells historically have been limited to wood. Wood suffers from the disadvantages of drying, cracking and inconsistent quality. Since drums are produced by laminating several plies of wood, delamination also can be a problem. Developments in composite materials have increased their versatility and offer the stiffness, low density, and uniformity required to be considered as a replacement for wood in musical instruments.
Hutchins of The Catgut Acoustical Society, Thompson of the C. F. Martin Company, and Haines of the University of South Carolina were among the first researchers to explore the possibilities of using composite materials in stringed instruments as top plates for violins and guitars. Their study involved an analysis of the vibrational deformation which occurs at the harmonic modes produced by the vibrating string. The mechanical properties of their top plates matched those of a conventional spruce plate. The use of composite materials in stringed instruments has been reported in U.S. Pat. No. 4,949,381. The Yamaha corporation recently reported on the construction of a composite prototype set of drums for a famous drummer. The drums, however, were constructed by a process other than the one now disclosed.
There is a distinct difference between the use of composite materials for the bodies of stringed instruments and drums. Stringed instruments have a definite tone due to the simple harmonic overtone structure that a vibrating string produces. These overtone frequencies are integral multiples of the fundamental frequency. Scientists' and engineers' knowledge of a strings vibration allows the determination of the required resonant frequencies for the design of a composite resonating structure.
The physics of drums is not as well understood. Only three reports formally address the physics of drums: a study in the 1930's by Raman of the modes of the Indian tabla, a small hand held drum; a study by Rossing in 1982 on the modes of a drumhead; and a later study by Rossing on the effect of air mass loading in a kettle drum on the modes of a drumhead (reported in Scientific American, 1982, volume 247). Rossing concluded that the drumheads modes are not integral multiples of each other, rather multiples of 1.59, 2.14, 2.3, 2.92, etc. None of the studies address the influence of the drumheads' modes on the drumshell or the drumshells' mechanical properties on the sound quality produced.
Extruded acrylic and polyvinylchloride drumshells have been reported, as well as one cast composite shell incorporating short glass fibers in an unsaturated polyester matrix. These were manufactured by processes other than filament winding and the materials used have no acoustic advantage. U.S. Pat. No. 4,282,793 describes a composite drum head, comprising polyaramide fiber fabric impregnated with a rigidifying amount of epoxy polymer. While this disclosure appreciates composites, it appears limited to the use of such in the drumhead membrane.